1. Field of the Invention
The present invention relates generally to an optical storage device, and more particularly to an actuator for an optical pickup in an optical disk drive.
2. Description of the Related Art
An optical disk has received attention as a memory medium that becomes a core in the recent rapid development of multimedia, and it is usually accommodated in a cartridge case to be provided as an optical disk cartridge for practical use. The optical disk cartridge is loaded into an optical disk drive to perform reading/writing of data from/to the optical disk by means of an optical pickup (optical head).
A recent optical disk drive intended to realize size reduction is composed of a fixed optical assembly including a laser diode module, a beam splitter for reflecting and transmitting a laser beam, and a photodetector for receiving reflected light from an optical disk, and a movable optical assembly including a carriage and an objective lens actuator mounted on the carriage and having an objective lens. The carriage is movable in the radial direction of the optical disk along a pair of rails by means of a voice coil motor (VCM). A write-power laser beam emitted from the laser diode of the fixed optical assembly is first collimated by a collimator lens, next transmitted by the beam splitter, next reflected by a beam raising mirror of the movable optical assembly, and finally focused on the optical disk by the objective lens, thereby writing data onto the optical disk. On the other hand, data reading is performed by directing a read-power laser beam onto the optical disk. Reflected light from the optical disk is first collimated by the objective lens, next reflected by the beam splitter, and finally detected by the photodetector, thereby converting the detected optical signal into an electrical signal.
The objective lens actuator includes an actuator base (fixed portion) fixed to the carriage, and a lens holder (movable portion) supported to the actuator base in a cantilever fashion by a plurality of spring wires or leaf springs. The lens holder has an objective lens, a focusing coil, and a plurality of tracking coils. A magnetic circuit opposed to the focusing coil and the tracking coils to configure the VCM is fixed to the actuator base or the carriage. The conventional objective lens actuator is assembled by the following method. First, the actuator base is temporarily fixed to the carriage by means of screws or the like. Secondly, the tilt of the actuator base or the tilt of a spindle motor for mounting the optical disk is adjusted so that the optical axis of the objective lens becomes substantially perpendicular to an ideal recording surface of the optical disk. Finally, the actuator base is fixed to the carriage.
For a proper reading and/or writing operation in an optical disk drive, a beam spot focused on the recording surface of the optical disk by the objective lens must be maintained always in an optimum shape. Accordingly, the laser beam must be directed onto the recording surface of the optical disk substantially perpendicularly thereto. To meet these requirements, the tilt of the actuator base or the tilt of the spindle motor is adjusted so that the optical axis of the objective lens becomes substantially perpendicular to the ideal recording surface of the optical disk in assembling the optical disk drive as described above. Further, the lens holder holding the objective lens undergoes a focusing operation to maintain an optimum beam spot shape during reading and/or writing of data, because there occur surface vibrations due to potential warpage or the like of the optical disk.
FIG. 1 is a graph showing the tilt of the optical axis of the objective lens in the radial direction of the optical disk in the case of displacing the lens holder in the focusing direction in the conventional objective lens actuator. As described above, the method of assembling the conventional objective lens actuator includes the steps of adjusting the tilt of the actuator base or the tilt of the spindle motor and thereafter fixing the actuator base to the carriage by means of screws or the like. As apparent from FIG. 1, the radial tilt of the optical axis of the objective lens (the tilt in the radial direction of the optical disk) increases with an increase in displacement of the lens holder in the focusing direction in the conventional assembling method. Accordingly, although the radial tilt (xe2x88x920.07xc2x0) is adjusted to 0 at the position where the displacement of the lens holder in the focusing direction is 0 (an ideal focal length to the ideal recording surface) by the tilt adjustment of the actuator base or the spindle motor, the radial tilt in relation to the displacement of the lens holder in the focusing direction remains, causing a possibility of adverse effects on a proper operation. The tilt of the optical axis of the objective lens in the radial direction of the optical disk in relation to the displacement of the lens holder in the focusing direction is expected to be due to the fact that there is a difference in rigidity between the horizontally opposite spring wires supporting the lens holder or that the point of action of the actuator in the focusing direction is offset from the center of gravity of the lens holder.
Thus, the conventional objective lens actuator involves the deviation in position between the center of gravity of the lens holder and the point of action of the actuator in performing a focusing operation, or the imbalance such as variations in spring rigidity between the elastic supporting members (e.g., leaf springs or spring wires) supporting the lens holder. As a result, the tilt of the optical axis of the objective lens occurs in association with a change in spatial position of the lens holder in performing a focusing operation. If the tilt of the optical axis of the objective lens increases, there is a possibility that a data reading and/or writing operation may be adversely affected.
It is therefore an object of the present invention to provide an optical storage device which can minimize the tilt of the optical axis of an objective lens occurring in performing a focusing operation.
In accordance with an aspect of the present invention, there is provided an optical storage device capable of at least reading information recorded on an optical storage medium, comprising an actuator base for movably supporting a movable portion holding an objective lens for focusing a light beam onto the optical storage medium; a fixing portion for fixing the actuator base; and a lens actuator for driving the objective lens to displace the objective lens at least in a focusing direction, the lens actuator comprising a coil provided on one of the movable portion and the fixing portion and a magnetic circuit provided on the other of the movable portion and the fixing portion; the actuator base being fixed to the fixing portion in the condition that a relative position between the coil and the magnetic circuit in a given direction is set so as to minimize the tilt of the optical axis of the objective lens in the given direction occurring in displacing the objective lens in the focusing direction.
The fixing portion comprises a carriage for moving the lens actuator across tracks formed on the optical storage medium. Preferably, one of the actuator base and the carriage has an elongated hole for adjustment of the relative position. The elongated hole extends in the given direction. The other of the actuator base and the carriage has an engaging member movably engaging with the elongated hole. The given direction is a direction across the tracks or a direction substantially along the tracks.
In accordance with another aspect of the present invention, there is provided an optical storage device capable of at least reading information recorded on an optical storage medium, comprising a drive base; a carriage mounted on the drive base so as to be reciprocatable in a first direction; first driving means for moving the carriage; a light source mounted on the drive base; and an objective lens actuator having an objective lens for focusing a light beam output from the light source onto the optical storage medium; the objective lens actuator comprising an actuator base fixed to the carriage; a lens holder for holding the objective lens; supporting means for movably supporting the lens holder to the actuator base; and second driving means for moving the objective lens in a focusing direction, the second driving means comprising a magnetic circuit fixed to the carriage and a coil fixed to the lens holder; wherein one of the actuator base and the carriage has an elongated hole extending in the first direction; a relative position between the actuator base and the carriage in the first direction is adjusted so that the tilt of the optical axis of the objective lens in the first direction occurring in displacing the lens holder in the focusing direction is minimized; and the actuator base is fixed to the carriage by fixing means inserted through the elongated hole.
In accordance with a further aspect of the present invention, there is provided an optical storage device capable of at least reading information recorded on an optical storage medium, comprising a drive base; a carriage mounted on the drive base so as to be reciprocatable in a first direction; first driving means for moving the carriage; a light source mounted on the drive base; and an objective lens actuator having an objective lens for focusing a light beam output from the light source onto the optical storage medium; the objective lens actuator comprising an actuator base fixed to the carriage; a lens holder for holding the objective lens; supporting means for movably supporting the lens holder to the actuator base; and second driving means for moving the objective lens in a focusing direction, the second driving means comprising a magnetic circuit fixed to the carriage and a coil fixed to the lens holder; wherein one of the actuator base and the carriage has an elongated hole extending in a second direction substantially perpendicular to the first direction; a relative position between the actuator base and the carriage in the second direction is adjusted so that the tilt of the optical axis of the objective lens in the second direction occurring in displacing the lens holder in the focusing direction is minimized; and the actuator base is fixed to the carriage by fixing means inserted through the elongated hole.
In accordance with a still further aspect of the present invention, there is provided a method of assembling an optical head including an actuator base for movably supporting a movable portion holding an objective lens for focusing a light beam onto an optical storage medium, a fixing portion for fixing the actuator base, and a lens actuator for driving the objective lens to displace the objective lens at least in a focusing direction, the lens actuator having a coil provided on one of the movable portion and the fixing portion and a magnetic circuit provided on the other of the movable portion and the fixing portion; the method comprising the steps of temporarily fixing the actuator base to the fixing portion; continuously reciprocating the objective lens in the focusing direction; measuring the tilt of the optical axis of the objective lens in a given direction; adjusting a relative position between the coil and the magnetic circuit in the given direction so that the tilt in the given direction is minimized; and finally fixing the actuator base to the fixing portion after the adjusting step.
The above and other objects, features and advantages of the present invention and the manner of realizing them will become more apparent, and the invention itself will best be understood from a study of the following description and appended claims with reference to the attached drawings showing some preferred embodiments of the invention.